Nutritional Quality of Wheat and Soil Work

Technical articles - National Center for Agroecology

Field crops Wheat Soil tillage Nutritional quality Shallow tillage after harvest Cover crops Diversification

Aerial photograph of Rothamsted trials, United Kingdom

Ensuring soil health through reduced soil disturbance and organic inputs has proven agronomic interest, but does this impact the nutritional quality of harvested wheat?

A decline in wheat nutritional quality over 160 years

The long-term Broadbalk trials in England (Rothamsted, since 1843) have allowed analysis of the evolution of mineral concentration in wheat over time.

On these plots with conventionally tilled soil, analyses show that the contents of zinc, iron, copper, and magnesium remained stable until the mid-1960s, before significantly dropping. This decline coincides with the introduction of high-yielding semi-dwarf varieties, selected for their short straw height to limit lodging and increase yields.

Source: Fan, 2008[1]

This phenomenon is mainly explained by a dilution effect: the higher the yield, the more minerals are diluted in an increased grain mass, without the plant absorbing more nutrients.

A decline without soil depletion

Contrary to what one might think, the decrease in mineral concentration in the grain does not come from soil depletion. Mineral concentrations in soils have remained stable or even increased, thanks to regular inputs of mineral fertilizers, organic matter, or atmospheric deposits. The observed effects are similar regardless of the type of fertilization (mineral, organic, or no fertilization).

Statistical analysis confirms that it is indeed plant-related factors – mainly the increase in yields due to varietal innovation – that explain the decrease in mineral concentration in grains.

Source: Garvin et al., 2006

These results align with those of other studies, notably American (Garvin et al., 2006) or Chinese (Xia et al., 2023), showing that the most recent varieties, often more productive, have lower micronutrient contents due to dilution.

Soil tillage, no-till, and nutritional quality

Cultural practices also influence nutritional quality, especially when they modify soil biology. For example, mycorrhization plays a key role in zinc absorption. Rotations including legumes, replacing fallow, generally improve grain protein and zinc contents. Diverse and perennial systems also promote better soil health, which can translate into better nutritional quality of wheat (Soil Health Institute, 2022).

An emerging point is ergothioneine (ERGO), an antioxidant produced by soil fungi and transmitted to plants via mycorrhizae. This antioxidant is beneficial for human health as it reduces inflammatory risk, lowers cardiovascular risk, and slows brain aging. A study conducted on a long-term trial (>40 years) showed that intensive plowing halves the ERGO content in wheat grain, while no-till promotes both mycorrhization and enrichment of the grain in ERGO, as well as in P, Mg, Cu, and Zn.

However, the impact of reduced tillage on the nutritional quality of crops remains generally limited. Another study on a comparative trial (Pearsons et al., 2022) showed that the type of cropping system (conventional or organic, with or without fertilization) had more impact on grain quality than the type of soil tillage. In this study, reduced tillage had no significant effect on protein or mineral content.

Finally, a recent comparison conducted in the Great West on 20 pairs of plots (no-till in conservation agriculture for 10 years vs conventional, same varieties) confirmed these observations: few differences on most minerals, but a significant increase in phosphorus, potassium, and ergothioneine in CA systems (Lefèvre et al., 2024).

Source: Lefèvre et al., 2024

Conclusion

1. The decline in mineral concentration in wheat is primarily linked to yield increases, by dilution, and not to soil depletion.
2. Fertilization, whether mineral or organic, has not stopped this trend.
3. Systems promoting mycorrhization (no-till, rotations with legumes) show potential to improve certain nutrients, including ergothioneine.
4. The type of cropping system influences nutritional quality more than soil tillage alone.